Counterflow vortex tubes and their method of operation are well known, such tubes being described, for example, in Fulton U.S. Pat. Nos. 3,173,273 and 3,208,229, and Ranque U.S. Pat. No. 1,952,281. Compressed air (or other gas) from any suitable source enters such a tube and is throttled through nozzles to produce the special temperature change effects which are the unique characteristics of a vortex tube. The result is that the compressed air entering the body of the tube is divided into hot and cold fractions discharged from outlets at opposite ends of the tube. Usually a vortex tube is used for the cold air produced with typical temperatures at the cold air outlet ranging from minus 40.degree. F. to plus 30.degree. F.
The cold air from vortex tubes has been used as a coolant in a wide variety of drilling, milling, sawing, and grinding applications. In such an installation, the vortex tube is ordinarily mounted in close proximity to the operating element (i.e., drill, saw, grinding wheel, etc.) with the cold air outlet of the tube pointed towards the workpiece. The cold air discharged from the tube prevents overheating of the workpiece as well as the operating element and, in addition, directs debris away from the work zone.
It has been recognized that heat build-up may also be a problem in commercial sewing machine operations where speeds of 5,000 stitches per minute or more are not uncommon. Frictional heat is generated as the sewing needle passes through the fabric and when the thread travels through the eye of the needle. Thread breakage, resulting in machine downtime and loss of productivity, may be occasioned because of burning or melting (in the case of synthetic materials) of the thread. In some cases the heating and softening of a synthetic thread may cause a clogging of the eye of the needle, thereby increasing frictional resistance and ultimate thread breakage. While undesirable heat build-up leading to thread breakage may occur when a sewing machine runs without interruption for extended periods the problem is also likely to occur when such a machine is operated intermittently with relatively short bursts at high operating speeds.
Efforts have been made to utilize vortex tube cooling devices to prevent thread breakage in the operation of industrial sewing machines but such efforts have met with only limited success. The mounting of a vortex tube adjacent the head of a sewing machine poses problems which vary according to the differences in configuration and design of different brands of machines but, even under the most favorable conditions, only limited mounting space is available and, when such space is occupied by a vortex tube, the added equipment may make operation of the sewing machine less convenient for the user. To provide a secure attachment of such a vortex tube at or near the head of the machine, it has been considered necessary to drill mounting holes into the machine, an operation which users may not be readily equipped to perform and which may in some cases damage or adversely affect operation of the machine.
One aspect of this invention therefore lies in recognizing that the problems associated with the use of a vortex tube to cool the needle of a sewing machine may be eliminated or greatly reduced by mounting the tube upon the worktable at a point remote from the sewing head and then directing cooling air from the remotely-located vortex tube through an insulated sound-muffling hose to a small nozzle mounted immediately adjacent the sewing needle. Because of its small size, the nozzle does not obstruct the user's view of the work area. In the best mode presently known for practicing the invention, the nozzle is mounted directly upon the pressure foot bushing and is provided with a plurality of vertically-spaced openings for directing a curtain of cooling air against the sewing needle.
The remote location of the vortex tube provides a number of important advantages in addition to keeping a relatively bulky component away from the work area. The hot air necessarily discharged from the vortex tube may be easily directed away from the user and in any event is not discharged into the immediate work area. The noise generated by the operation of the vortex tube is less objectionable, first, because, the tube is spaced a substantial distance away from the user, and second, because the elongated hose leading from the remote vortex tube to the discharge nozzle also functions as a noise-abating muffler. The insulation responsible for damping the noise generated by the vortex tube also functions as thermal insulation. Therefore, despite the fact that cold air is conducted a substantial distance through the hose from the remote vortex tube to the nozzle, the heat and humidity sometimes encountered in factories where garments are made is less likely to cause condensation that might otherwise drip from the hose and mar or damage the article being sewn.
Because of its small size and its attachment directly to the pressure foot bushing, the vertically-elongated nozzle with its lateral discharge ports does not obstruct or interfere with operation of the machine or with the movement of fabric beneath the sewing head. A control member in the form of a sleeve is slidably mounted upon the nozzle tube for deflecting or blocking the flow of air from some or all of the orifices when such flow might interfere with threading of the needle or with some other preliminary operations involving the needle and its associated elements.
Other features, advantages, and objects of the invention will become apparent from the specification and drawings.